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 $112.62   4.154%   $117.2982   $117.30   $117.30   $117.30  
  Purchase #2 $211.86   4.281%   $220.9297   $220.93   $220.95   $220.90  
  Purchase #3 $96.76   5.833%   $102.404   $102.40   $102.40   $102.40  
  Purchase #4 $138.31   11.146%   $153.726   $153.73   $153.75   $153.70  
  Purchase #5 $84.65   9.353%   $92.5673   $92.57   $92.55   $92.60  
  Purchase #6 $170.65   3.344%   $176.3565   $176.36   $176.35   $176.40  
  Purchase #7 $118.97   12.611%   $133.9733   $133.97   $133.95   $134.00  
  7 purchase totals = $933.82       $997.2550   $997.26   $997.25   $997.30