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 $193.97   10.154%   $213.6657   $213.67   $213.65   $213.70  
  Purchase #2 $82.67   5.234%   $86.9969   $87.00   $87.00   $87.00  
  Purchase #3 $144.56   3.547%   $149.6875   $149.69   $149.70   $149.70  
  Purchase #4 $226.41   9.504%   $247.928   $247.93   $247.95   $247.90  
  Purchase #5 $28.80   4.109%   $29.9834   $29.98   $30.00   $30.00  
  Purchase #6 $121.76   9.629%   $133.4843   $133.48   $133.50   $133.50  
  Purchase #7 $166.78   4.109%   $173.633   $173.63   $173.65   $173.60  
  7 purchase totals = $964.95       $1,035.3788   $1,035.38   $1,035.45   $1,035.40