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 $233.26   13.815%   $265.4849   $265.48   $265.50   $265.50  
  Purchase #2 $227.52   12.500%   $255.96   $255.96   $255.95   $256.00  
  Purchase #3 $56.94   12.377%   $63.9875   $63.99   $64.00   $64.00  
  Purchase #4 $93.78   11.235%   $104.3162   $104.32   $104.30   $104.30  
  Purchase #5 $200.65   4.761%   $210.2029   $210.20   $210.20   $210.20  
  Purchase #6 $167.51   9.356%   $183.1822   $183.18   $183.20   $183.20  
  Purchase #7 $104.92   11.439%   $116.9218   $116.92   $116.90   $116.90  
  7 purchase totals = $1,084.58       $1,200.0555   $1,200.05   $1,200.05   $1,200.10