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 $124.72   8.181%   $134.9233   $134.92   $134.90   $134.90  
  Purchase #2 $199.38   13.435%   $226.1667   $226.17   $226.15   $226.20  
  Purchase #3 $13.33   9.559%   $14.6042   $14.60   $14.60   $14.60  
  Purchase #4 $52.27   3.205%   $53.9453   $53.95   $53.95   $53.90  
  Purchase #5 $145.32   7.419%   $156.1013   $156.10   $156.10   $156.10  
  Purchase #6 $194.83   4.688%   $203.9636   $203.96   $203.95   $204.00  
  Purchase #7 $111.63   11.703%   $124.6941   $124.69   $124.70   $124.70  
  7 purchase totals = $841.48       $914.3985   $914.39   $914.35   $914.40