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 $118.40   5.159%   $124.5083   $124.51   $124.50   $124.50  
  Purchase #2 $158.42   11.507%   $176.6494   $176.65   $176.65   $176.60  
  Purchase #3 $213.76   12.816%   $241.1555   $241.16   $241.15   $241.20  
  Purchase #4 $189.38   5.484%   $199.7656   $199.77   $199.75   $199.80  
  Purchase #5 $227.61   8.325%   $246.5585   $246.56   $246.55   $246.60  
  Purchase #6 $180.84   8.550%   $196.3018   $196.30   $196.30   $196.30  
  Purchase #7 $65.85   13.861%   $74.9775   $74.98   $75.00   $75.00  
  7 purchase totals = $1,154.26       $1,259.9166   $1,259.93   $1,259.90   $1,260.00