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 $243.38   5.716%   $257.2916   $257.29   $257.30   $257.30  
  Purchase #2 $112.51   4.492%   $117.5639   $117.56   $117.55   $117.60  
  Purchase #3 $132.30   8.266%   $143.2359   $143.24   $143.25   $143.20  
  Purchase #4 $177.49   13.226%   $200.9648   $200.96   $200.95   $201.00  
  Purchase #5 $220.79   8.633%   $239.8508   $239.85   $239.85   $239.90  
  Purchase #6 $184.72   4.752%   $193.4979   $193.50   $193.50   $193.50  
  Purchase #7 $84.92   6.588%   $90.5145   $90.51   $90.50   $90.50  
  7 purchase totals = $1,156.11       $1,242.9194   $1,242.91   $1,242.90   $1,243.00