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 $48.92   5.297%   $51.5113   $51.51   $51.50   $51.50  
  Purchase #2 $121.69   6.523%   $129.6278   $129.63   $129.65   $129.60  
  Purchase #3 $22.73   11.800%   $25.4121   $25.41   $25.40   $25.40  
  Purchase #4 $154.70   9.239%   $168.9927   $168.99   $169.00   $169.00  
  Purchase #5 $192.74   5.606%   $203.545   $203.55   $203.55   $203.50  
  Purchase #6 $75.83   12.538%   $85.3376   $85.34   $85.35   $85.30  
  Purchase #7 $83.97   9.429%   $91.8875   $91.89   $91.90   $91.90  
  7 purchase totals = $700.58       $756.3140   $756.32   $756.35   $756.20