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 $94.98   8.269%   $102.8339   $102.83   $102.85   $102.80  
  Purchase #2 $145.87   12.339%   $163.8689   $163.87   $163.85   $163.90  
  Purchase #3 $152.52   9.351%   $166.7821   $166.78   $166.80   $166.80  
  Purchase #4 $97.41   5.117%   $102.3945   $102.39   $102.40   $102.40  
  Purchase #5 $179.26   13.848%   $204.0839   $204.08   $204.10   $204.10  
  Purchase #6 $132.73   10.240%   $146.3216   $146.32   $146.30   $146.30  
  Purchase #7 $63.99   4.146%   $66.643   $66.64   $66.65   $66.60  
  7 purchase totals = $866.76       $952.9279   $952.91   $952.95   $952.90