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 $87.58   7.718%   $94.3394   $94.34   $94.35   $94.30  
  Purchase #2 $64.48   13.709%   $73.3196   $73.32   $73.30   $73.30  
  Purchase #3 $163.44   5.540%   $172.4946   $172.49   $172.50   $172.50  
  Purchase #4 $216.56   5.190%   $227.7995   $227.80   $227.80   $227.80  
  Purchase #5 $110.51   12.174%   $123.9635   $123.96   $123.95   $124.00  
  Purchase #6 $117.49   11.591%   $131.1083   $131.11   $131.10   $131.10  
  Purchase #7 $78.58   12.815%   $88.65   $88.65   $88.65   $88.70  
  7 purchase totals = $838.64       $911.6749   $911.67   $911.65   $911.70