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 $33.97   9.749%   $37.2817   $37.28   $37.30   $37.30  
  Purchase #2 $218.96   7.206%   $234.7383   $234.74   $234.75   $234.70  
  Purchase #3 $114.95   11.206%   $127.8313   $127.83   $127.85   $127.80  
  Purchase #4 $6.67   7.585%   $7.1759   $7.18   $7.20   $7.20  
  Purchase #5 $155.83   13.488%   $176.8484   $176.85   $176.85   $176.80  
  Purchase #6 $229.92   13.356%   $260.6281   $260.63   $260.65   $260.60  
  Purchase #7 $178.86   6.555%   $190.5843   $190.58   $190.60   $190.60  
  7 purchase totals = $939.16       $1,035.0880   $1,035.09   $1,035.20   $1,035.00