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 $82.74   6.554%   $88.1628   $88.16   $88.15   $88.20  
  Purchase #2 $198.78   5.609%   $209.9296   $209.93   $209.95   $209.90  
  Purchase #3 $135.86   10.710%   $150.4106   $150.41   $150.40   $150.40  
  Purchase #4 $144.92   6.784%   $154.7514   $154.75   $154.75   $154.80  
  Purchase #5 $32.38   5.265%   $34.0848   $34.08   $34.10   $34.10  
  Purchase #6 $191.68   8.537%   $208.0437   $208.04   $208.05   $208.00  
  Purchase #7 $167.66   7.361%   $180.0015   $180.00   $180.00   $180.00  
  7 purchase totals = $954.02       $1,025.3844   $1,025.37   $1,025.40   $1,025.40