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 $117.39   8.164%   $126.9737   $126.97   $126.95   $127.00  
  Purchase #2 $112.59   5.170%   $118.4109   $118.41   $118.40   $118.40  
  Purchase #3 $66.34   3.671%   $68.7753   $68.78   $68.80   $68.80  
  Purchase #4 $82.41   13.469%   $93.5098   $93.51   $93.50   $93.50  
  Purchase #5 $61.96   5.454%   $65.3393   $65.34   $65.35   $65.30  
  Purchase #6 $206.40   6.448%   $219.7087   $219.71   $219.70   $219.70  
  Purchase #7 $212.30   13.424%   $240.7992   $240.80   $240.80   $240.80  
  7 purchase totals = $859.39       $933.5169   $933.52   $933.50   $933.50