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 $97.49   4.707%   $102.0789   $102.08   $102.10   $102.10  
  Purchase #2 $156.41   6.253%   $166.1903   $166.19   $166.20   $166.20  
  Purchase #3 $25.86   7.565%   $27.8163   $27.82   $27.80   $27.80  
  Purchase #4 $74.86   12.557%   $84.2602   $84.26   $84.25   $84.30  
  Purchase #5 $206.46   7.692%   $222.3409   $222.34   $222.35   $222.30  
  Purchase #6 $224.26   6.214%   $238.1955   $238.20   $238.20   $238.20  
  Purchase #7 $174.64   11.109%   $194.0408   $194.04   $194.05   $194.00  
  7 purchase totals = $959.98       $1,034.9229   $1,034.93   $1,034.95   $1,034.90