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 $113.81   4.173%   $118.5593   $118.56   $118.55   $118.60  
  Purchase #2 $169.87   9.118%   $185.3587   $185.36   $185.35   $185.40  
  Purchase #3 $68.76   7.684%   $74.0435   $74.04   $74.05   $74.00  
  Purchase #4 $155.67   3.438%   $161.0219   $161.02   $161.00   $161.00  
  Purchase #5 $219.77   11.753%   $245.5996   $245.60   $245.60   $245.60  
  Purchase #6 $6.76   12.845%   $7.6283   $7.63   $7.65   $7.60  
  Purchase #7 $212.28   6.325%   $225.7067   $225.71   $225.70   $225.70  
  7 purchase totals = $946.92       $1,017.9180   $1,017.92   $1,017.90   $1,017.90