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 $58.52   5.634%   $61.817   $61.82   $61.80   $61.80  
  Purchase #2 $44.35   10.299%   $48.9176   $48.92   $48.90   $48.90  
  Purchase #3 $167.72   10.458%   $185.2602   $185.26   $185.25   $185.30  
  Purchase #4 $67.88   9.691%   $74.4583   $74.46   $74.45   $74.50  
  Purchase #5 $29.68   13.689%   $33.7429   $33.74   $33.75   $33.70  
  Purchase #6 $169.98   10.557%   $187.9248   $187.92   $187.90   $187.90  
  Purchase #7 $161.92   12.191%   $181.6597   $181.66   $181.65   $181.70  
  7 purchase totals = $700.05       $773.7805   $773.78   $773.70   $773.80