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 $70.84   7.154%   $75.9079   $75.91   $75.90   $75.90  
  Purchase #2 $200.30   13.581%   $227.5027   $227.50   $227.50   $227.50  
  Purchase #3 $51.27   4.436%   $53.5443   $53.54   $53.55   $53.50  
  Purchase #4 $245.74   4.486%   $256.7639   $256.76   $256.75   $256.80  
  Purchase #5 $30.47   9.147%   $33.2571   $33.26   $33.25   $33.30  
  Purchase #6 $244.54   10.778%   $270.8965   $270.90   $270.90   $270.90  
  Purchase #7 $84.92   10.761%   $94.0582   $94.06   $94.05   $94.10  
  7 purchase totals = $928.08       $1,011.9306   $1,011.93   $1,011.90   $1,012.00