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 $94.71   4.427%   $98.9028   $98.90   $98.90   $98.90  
  Purchase #2 $60.25   4.275%   $62.8257   $62.83   $62.85   $62.80  
  Purchase #3 $140.57   9.541%   $153.9818   $153.98   $154.00   $154.00  
  Purchase #4 $226.79   13.591%   $257.613   $257.61   $257.60   $257.60  
  Purchase #5 $171.38   10.671%   $189.668   $189.67   $189.65   $189.70  
  Purchase #6 $244.82   10.498%   $270.5212   $270.52   $270.50   $270.50  
  Purchase #7 $227.98   4.250%   $237.6692   $237.67   $237.65   $237.70  
  7 purchase totals = $1,166.50       $1,271.1817   $1,271.18   $1,271.15   $1,271.20