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 $88.91   5.761%   $94.0321   $94.03   $94.05   $94.00  
  Purchase #2 $133.73   13.625%   $151.9507   $151.95   $151.95   $152.00  
  Purchase #3 $202.76   6.225%   $215.3818   $215.38   $215.40   $215.40  
  Purchase #4 $49.34   4.826%   $51.7211   $51.72   $51.70   $51.70  
  Purchase #5 $25.26   10.386%   $27.8835   $27.88   $27.90   $27.90  
  Purchase #6 $141.79   3.681%   $147.0093   $147.01   $147.00   $147.00  
  Purchase #7 $109.66   3.264%   $113.2393   $113.24   $113.25   $113.20  
  7 purchase totals = $751.45       $801.2178   $801.21   $801.25   $801.20