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 $88.82   5.853%   $94.0186   $94.02   $94.00   $94.00  
  Purchase #2 $102.72   7.109%   $110.0224   $110.02   $110.00   $110.00  
  Purchase #3 $195.91   5.304%   $206.3011   $206.30   $206.30   $206.30  
  Purchase #4 $220.57   10.329%   $243.3527   $243.35   $243.35   $243.40  
  Purchase #5 $24.86   11.205%   $27.6456   $27.65   $27.65   $27.60  
  Purchase #6 $176.35   8.267%   $190.9289   $190.93   $190.95   $190.90  
  Purchase #7 $80.31   13.434%   $91.0988   $91.10   $91.10   $91.10  
  7 purchase totals = $889.54       $963.3681   $963.37   $963.35   $963.30