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 $62.94   5.705%   $66.5307   $66.53   $66.55   $66.50  
  Purchase #2 $194.94   4.115%   $202.9618   $202.96   $202.95   $203.00  
  Purchase #3 $71.43   6.787%   $76.278   $76.28   $76.30   $76.30  
  Purchase #4 $221.48   8.224%   $239.6945   $239.69   $239.70   $239.70  
  Purchase #5 $22.52   12.839%   $25.4113   $25.41   $25.40   $25.40  
  Purchase #6 $19.69   6.563%   $20.9823   $20.98   $21.00   $21.00  
  Purchase #7 $205.34   10.297%   $226.4839   $226.48   $226.50   $226.50  
  7 purchase totals = $798.34       $858.3425   $858.33   $858.40   $858.40