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 $152.85   8.724%   $166.1846   $166.18   $166.20   $166.20  
  Purchase #2 $204.66   9.618%   $224.3442   $224.34   $224.35   $224.30  
  Purchase #3 $247.90   12.204%   $278.1537   $278.15   $278.15   $278.20  
  Purchase #4 $238.81   3.411%   $246.9558   $246.96   $246.95   $247.00  
  Purchase #5 $32.50   5.457%   $34.2735   $34.27   $34.25   $34.30  
  Purchase #6 $235.95   8.292%   $255.515   $255.52   $255.50   $255.50  
  Purchase #7 $151.70   12.674%   $170.9265   $170.93   $170.95   $170.90  
  7 purchase totals = $1,264.37       $1,376.3533   $1,376.35   $1,376.35   $1,376.40