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 $213.59   13.323%   $242.0466   $242.05   $242.05   $242.00  
  Purchase #2 $74.50   12.721%   $83.9771   $83.98   $84.00   $84.00  
  Purchase #3 $121.58   8.669%   $132.1198   $132.12   $132.10   $132.10  
  Purchase #4 $104.66   13.607%   $118.9011   $118.90   $118.90   $118.90  
  Purchase #5 $187.51   6.774%   $200.2119   $200.21   $200.20   $200.20  
  Purchase #6 $149.66   4.278%   $156.0625   $156.06   $156.05   $156.10  
  Purchase #7 $75.27   5.104%   $79.1118   $79.11   $79.10   $79.10  
  7 purchase totals = $926.77       $1,012.4308   $1,012.43   $1,012.40   $1,012.40