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 $64.74   13.191%   $73.2799   $73.28   $73.30   $73.30  
  Purchase #2 $28.85   13.317%   $32.692   $32.69   $32.70   $32.70  
  Purchase #3 $57.26   10.512%   $63.2792   $63.28   $63.30   $63.30  
  Purchase #4 $111.57   7.593%   $120.0415   $120.04   $120.05   $120.00  
  Purchase #5 $235.36   4.350%   $245.5982   $245.60   $245.60   $245.60  
  Purchase #6 $84.41   10.231%   $93.046   $93.05   $93.05   $93.00  
  Purchase #7 $193.32   3.512%   $200.1094   $200.11   $200.10   $200.10  
  7 purchase totals = $775.51       $828.0462   $828.05   $828.10   $828.00