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 $47.26   8.401%   $51.2303   $51.23   $51.25   $51.20  
  Purchase #2 $188.91   9.653%   $207.1455   $207.15   $207.15   $207.10  
  Purchase #3 $10.25   12.568%   $11.5382   $11.54   $11.55   $11.50  
  Purchase #4 $202.93   8.476%   $220.1303   $220.13   $220.15   $220.10  
  Purchase #5 $201.37   10.411%   $222.3346   $222.33   $222.35   $222.30  
  Purchase #6 $170.60   8.735%   $185.5019   $185.50   $185.50   $185.50  
  Purchase #7 $62.66   10.727%   $69.3815   $69.38   $69.40   $69.40  
  7 purchase totals = $883.98       $967.2623   $967.26   $967.35   $967.10