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 $203.46   4.611%   $212.8415   $212.84   $212.85   $212.80  
  Purchase #2 $31.39   4.829%   $32.9058   $32.91   $32.90   $32.90  
  Purchase #3 $99.39   3.207%   $102.5774   $102.58   $102.60   $102.60  
  Purchase #4 $175.79   12.510%   $197.7813   $197.78   $197.80   $197.80  
  Purchase #5 $104.45   8.763%   $113.603   $113.60   $113.60   $113.60  
  Purchase #6 $247.58   7.545%   $266.2599   $266.26   $266.25   $266.30  
  Purchase #7 $118.97   3.579%   $123.2279   $123.23   $123.25   $123.20  
  7 purchase totals = $981.03       $1,049.1968   $1,049.20   $1,049.25   $1,049.20