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 $203.51   6.604%   $216.9498   $216.95   $216.95   $216.90  
  Purchase #2 $36.27   3.555%   $37.5594   $37.56   $37.55   $37.60  
  Purchase #3 $182.32   11.528%   $203.3378   $203.34   $203.35   $203.30  
  Purchase #4 $124.79   5.244%   $131.334   $131.33   $131.35   $131.30  
  Purchase #5 $24.98   6.675%   $26.6474   $26.65   $26.65   $26.60  
  Purchase #6 $211.38   8.572%   $229.4995   $229.50   $229.50   $229.50  
  Purchase #7 $119.86   7.374%   $128.6985   $128.70   $128.70   $128.70  
  7 purchase totals = $903.11       $974.0264   $974.03   $974.05   $973.90