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 $60.97   4.183%   $63.5204   $63.52   $63.50   $63.50  
  Purchase #2 $84.65   3.347%   $87.4832   $87.48   $87.50   $87.50  
  Purchase #3 $149.80   13.549%   $170.0964   $170.10   $170.10   $170.10  
  Purchase #4 $203.56   6.400%   $216.5878   $216.59   $216.60   $216.60  
  Purchase #5 $5.98   4.679%   $6.2598   $6.26   $6.25   $6.30  
  Purchase #6 $153.56   8.772%   $167.0303   $167.03   $167.05   $167.00  
  Purchase #7 $103.48   7.652%   $111.3983   $111.40   $111.40   $111.40  
  7 purchase totals = $762.00       $822.3762   $822.38   $822.40   $822.40