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 $134.58   9.664%   $147.5858   $147.59   $147.60   $147.60  
  Purchase #2 $202.91   4.633%   $212.3108   $212.31   $212.30   $212.30  
  Purchase #3 $65.60   7.211%   $70.3304   $70.33   $70.35   $70.30  
  Purchase #4 $247.37   8.238%   $267.7483   $267.75   $267.75   $267.70  
  Purchase #5 $209.70   12.452%   $235.8118   $235.81   $235.80   $235.80  
  Purchase #6 $236.46   4.634%   $247.4176   $247.42   $247.40   $247.40  
  Purchase #7 $72.57   6.682%   $77.4191   $77.42   $77.40   $77.40  
  7 purchase totals = $1,169.19       $1,258.6238   $1,258.63   $1,258.60   $1,258.50