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 $24.64   7.645%   $26.5237   $26.52   $26.50   $26.50  
  Purchase #2 $223.81   4.553%   $234.0001   $234.00   $234.00   $234.00  
  Purchase #3 $108.72   10.610%   $120.2552   $120.26   $120.25   $120.30  
  Purchase #4 $180.71   7.307%   $193.9145   $193.91   $193.90   $193.90  
  Purchase #5 $97.30   11.582%   $108.5693   $108.57   $108.55   $108.60  
  Purchase #6 $43.67   3.302%   $45.112   $45.11   $45.10   $45.10  
  Purchase #7 $88.41   3.488%   $91.4937   $91.49   $91.50   $91.50  
  7 purchase totals = $767.26       $819.8685   $819.86   $819.80   $819.90