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 $47.52   10.310%   $52.4193   $52.42   $52.40   $52.40  
  Purchase #2 $170.58   7.643%   $183.6174   $183.62   $183.60   $183.60  
  Purchase #3 $194.74   10.544%   $215.2734   $215.27   $215.25   $215.30  
  Purchase #4 $26.63   3.698%   $27.6148   $27.61   $27.60   $27.60  
  Purchase #5 $18.35   3.743%   $19.0368   $19.04   $19.05   $19.00  
  Purchase #6 $210.72   11.363%   $234.6641   $234.66   $234.65   $234.70  
  Purchase #7 $200.31   8.781%   $217.8992   $217.90   $217.90   $217.90  
  7 purchase totals = $868.85       $950.5250   $950.52   $950.45   $950.50