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 $111.98   11.318%   $124.6539   $124.65   $124.65   $124.70  
  Purchase #2 $193.57   8.319%   $209.6731   $209.67   $209.65   $209.70  
  Purchase #3 $62.70   12.707%   $70.6673   $70.67   $70.65   $70.70  
  Purchase #4 $86.52   8.267%   $93.6726   $93.67   $93.65   $93.70  
  Purchase #5 $235.35   11.501%   $262.4176   $262.42   $262.40   $262.40  
  Purchase #6 $148.35   12.437%   $166.8003   $166.80   $166.80   $166.80  
  Purchase #7 $132.52   9.768%   $145.4646   $145.46   $145.45   $145.50  
  7 purchase totals = $970.99       $1,073.3494   $1,073.34   $1,073.25   $1,073.50