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 $60.43   9.268%   $66.0307   $66.03   $66.05   $66.00  
  Purchase #2 $182.76   12.340%   $205.3126   $205.31   $205.30   $205.30  
  Purchase #3 $67.52   6.186%   $71.6968   $71.70   $71.70   $71.70  
  Purchase #4 $92.61   10.558%   $102.3878   $102.39   $102.40   $102.40  
  Purchase #5 $11.72   4.407%   $12.2365   $12.24   $12.25   $12.20  
  Purchase #6 $26.99   8.713%   $29.3416   $29.34   $29.35   $29.30  
  Purchase #7 $244.32   10.176%   $269.182   $269.18   $269.20   $269.20  
  7 purchase totals = $686.35       $756.1880   $756.19   $756.25   $756.10