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 $105.82   11.673%   $118.1724   $118.17   $118.15   $118.20  
  Purchase #2 $110.37   9.297%   $120.6311   $120.63   $120.65   $120.60  
  Purchase #3 $101.44   9.259%   $110.8323   $110.83   $110.85   $110.80  
  Purchase #4 $112.31   9.419%   $122.8885   $122.89   $122.90   $122.90  
  Purchase #5 $96.65   12.317%   $108.5544   $108.55   $108.55   $108.60  
  Purchase #6 $47.96   4.276%   $50.0108   $50.01   $50.00   $50.00  
  Purchase #7 $227.62   3.789%   $236.2445   $236.24   $236.25   $236.20  
  7 purchase totals = $802.17       $867.3340   $867.32   $867.35   $867.30