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 $39.35   11.556%   $43.8973   $43.90   $43.90   $43.90  
  Purchase #2 $239.98   11.522%   $267.6305   $267.63   $267.65   $267.60  
  Purchase #3 $82.33   13.851%   $93.7335   $93.73   $93.75   $93.70  
  Purchase #4 $206.33   6.193%   $219.108   $219.11   $219.10   $219.10  
  Purchase #5 $128.89   5.224%   $135.6232   $135.62   $135.60   $135.60  
  Purchase #6 $104.45   8.494%   $113.322   $113.32   $113.30   $113.30  
  Purchase #7 $68.97   7.315%   $74.0152   $74.02   $74.00   $74.00  
  7 purchase totals = $870.30       $947.3297   $947.33   $947.30   $947.20