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 $49.58   13.469%   $56.2579   $56.26   $56.25   $56.30  
  Purchase #2 $201.98   11.702%   $225.6157   $225.62   $225.60   $225.60  
  Purchase #3 $105.79   11.405%   $117.8553   $117.86   $117.85   $117.90  
  Purchase #4 $163.59   3.371%   $169.1046   $169.10   $169.10   $169.10  
  Purchase #5 $138.45   7.458%   $148.7756   $148.78   $148.80   $148.80  
  Purchase #6 $61.99   6.671%   $66.1254   $66.13   $66.15   $66.10  
  Purchase #7 $153.76   13.762%   $174.9205   $174.92   $174.90   $174.90  
  7 purchase totals = $875.14       $958.6550   $958.67   $958.65   $958.70