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 $33.44   10.113%   $36.8218   $36.82   $36.80   $36.80  
  Purchase #2 $217.95   13.165%   $246.6431   $246.64   $246.65   $246.60  
  Purchase #3 $68.58   7.128%   $73.4684   $73.47   $73.45   $73.50  
  Purchase #4 $213.42   10.375%   $235.5623   $235.56   $235.55   $235.60  
  Purchase #5 $201.85   3.574%   $209.0641   $209.06   $209.05   $209.10  
  Purchase #6 $102.39   3.113%   $105.5774   $105.58   $105.60   $105.60  
  Purchase #7 $148.47   12.313%   $166.7511   $166.75   $166.75   $166.80  
  7 purchase totals = $986.10       $1,073.8882   $1,073.88   $1,073.85   $1,074.00