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 $243.78   9.734%   $267.5095   $267.51   $267.50   $267.50  
  Purchase #2 $6.45   11.874%   $7.2159   $7.22   $7.20   $7.20  
  Purchase #3 $234.82   5.415%   $247.5355   $247.54   $247.55   $247.50  
  Purchase #4 $164.27   11.171%   $182.6206   $182.62   $182.60   $182.60  
  Purchase #5 $24.97   13.252%   $28.279   $28.28   $28.30   $28.30  
  Purchase #6 $74.63   7.433%   $80.1772   $80.18   $80.20   $80.20  
  Purchase #7 $49.39   11.235%   $54.939   $54.94   $54.95   $54.90  
  7 purchase totals = $798.31       $868.2767   $868.29   $868.30   $868.20