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 $164.92   10.796%   $182.7248   $182.72   $182.70   $182.70  
  Purchase #2 $160.48   4.778%   $168.1477   $168.15   $168.15   $168.10  
  Purchase #3 $45.99   4.420%   $48.0228   $48.02   $48.00   $48.00  
  Purchase #4 $58.48   9.221%   $63.8724   $63.87   $63.85   $63.90  
  Purchase #5 $214.58   4.662%   $224.5837   $224.58   $224.60   $224.60  
  Purchase #6 $34.43   6.861%   $36.7922   $36.79   $36.80   $36.80  
  Purchase #7 $16.46   5.416%   $17.3515   $17.35   $17.35   $17.40  
  7 purchase totals = $695.34       $741.4951   $741.48   $741.45   $741.50