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 $53.26   5.261%   $56.062   $56.06   $56.05   $56.10  
  Purchase #2 $91.97   5.236%   $96.7855   $96.79   $96.80   $96.80  
  Purchase #3 $76.58   13.796%   $87.145   $87.15   $87.15   $87.10  
  Purchase #4 $93.42   9.789%   $102.5649   $102.56   $102.55   $102.60  
  Purchase #5 $184.32   10.663%   $203.974   $203.97   $203.95   $204.00  
  Purchase #6 $122.25   4.621%   $127.8992   $127.90   $127.90   $127.90  
  Purchase #7 $239.50   8.604%   $260.1066   $260.11   $260.10   $260.10  
  7 purchase totals = $861.30       $934.5372   $934.54   $934.50   $934.60