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 $212.60   6.431%   $226.2723   $226.27   $226.25   $226.30  
  Purchase #2 $224.94   11.364%   $250.5022   $250.50   $250.50   $250.50  
  Purchase #3 $65.92   10.761%   $73.0137   $73.01   $73.00   $73.00  
  Purchase #4 $151.33   11.699%   $169.0341   $169.03   $169.05   $169.00  
  Purchase #5 $206.43   5.557%   $217.9013   $217.90   $217.90   $217.90  
  Purchase #6 $181.26   10.322%   $199.9697   $199.97   $199.95   $200.00  
  Purchase #7 $35.55   7.732%   $38.2987   $38.30   $38.30   $38.30  
  7 purchase totals = $1,078.03       $1,174.9920   $1,174.98   $1,174.95   $1,175.00