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 $240.54   10.367%   $265.4768   $265.48   $265.50   $265.50  
  Purchase #2 $179.51   7.316%   $192.643   $192.64   $192.65   $192.60  
  Purchase #3 $186.67   4.229%   $194.5643   $194.56   $194.55   $194.60  
  Purchase #4 $64.85   6.638%   $69.1547   $69.15   $69.15   $69.20  
  Purchase #5 $35.52   3.373%   $36.7181   $36.72   $36.70   $36.70  
  Purchase #6 $24.36   12.296%   $27.3553   $27.36   $27.35   $27.40  
  Purchase #7 $131.31   4.286%   $136.9379   $136.94   $136.95   $136.90  
  7 purchase totals = $862.76       $922.8501   $922.85   $922.85   $922.90