Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $124.93   8.694%   $135.7914   $135.79   $135.80   $135.80  
  Purchase #2 $213.93   10.121%   $235.5819   $235.58   $235.60   $235.60  
  Purchase #3 $132.64   4.258%   $138.2878   $138.29   $138.30   $138.30  
  Purchase #4 $118.77   4.743%   $124.4033   $124.40   $124.40   $124.40  
  Purchase #5 $234.89   10.132%   $258.6891   $258.69   $258.70   $258.70  
  Purchase #6 $194.84   11.811%   $217.8526   $217.85   $217.85   $217.90  
  Purchase #7 $225.59   4.679%   $236.1454   $236.15   $236.15   $236.10  
  7 purchase totals = $1,245.59       $1,346.7515   $1,346.75   $1,346.80   $1,346.80