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 $58.76   7.637%   $63.2475   $63.25   $63.25   $63.20  
  Purchase #2 $47.84   10.239%   $52.7383   $52.74   $52.75   $52.70  
  Purchase #3 $106.88   4.263%   $111.4363   $111.44   $111.45   $111.40  
  Purchase #4 $41.31   12.695%   $46.5543   $46.55   $46.55   $46.60  
  Purchase #5 $81.45   7.634%   $87.6679   $87.67   $87.65   $87.70  
  Purchase #6 $233.32   3.300%   $241.0196   $241.02   $241.00   $241.00  
  Purchase #7 $212.34   8.128%   $229.599   $229.60   $229.60   $229.60  
  7 purchase totals = $781.90       $832.2629   $832.27   $832.25   $832.20