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 $52.48   12.474%   $59.0264   $59.03   $59.05   $59.00  
  Purchase #2 $163.71   4.269%   $170.6988   $170.70   $170.70   $170.70  
  Purchase #3 $125.97   11.267%   $140.163   $140.16   $140.15   $140.20  
  Purchase #4 $100.32   11.359%   $111.7153   $111.72   $111.70   $111.70  
  Purchase #5 $189.39   12.827%   $213.6831   $213.68   $213.70   $213.70  
  Purchase #6 $123.62   8.827%   $134.5319   $134.53   $134.55   $134.50  
  Purchase #7 $172.57   11.386%   $192.2188   $192.22   $192.20   $192.20  
  7 purchase totals = $928.06       $1,022.0373   $1,022.04   $1,022.05   $1,022.00