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 $87.93   7.634%   $94.6426   $94.64   $94.65   $94.60  
  Purchase #2 $83.67   13.469%   $94.9395   $94.94   $94.95   $94.90  
  Purchase #3 $157.89   12.151%   $177.0752   $177.08   $177.10   $177.10  
  Purchase #4 $12.25   13.303%   $13.8796   $13.88   $13.90   $13.90  
  Purchase #5 $174.78   9.465%   $191.3229   $191.32   $191.30   $191.30  
  Purchase #6 $231.85   8.249%   $250.9753   $250.98   $251.00   $251.00  
  Purchase #7 $229.73   3.465%   $237.6901   $237.69   $237.70   $237.70  
  7 purchase totals = $978.10       $1,060.5252   $1,060.53   $1,060.60   $1,060.50