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 $245.93   7.747%   $264.9822   $264.98   $265.00   $265.00  
  Purchase #2 $238.91   6.601%   $254.6804   $254.68   $254.70   $254.70  
  Purchase #3 $146.29   6.587%   $155.9261   $155.93   $155.95   $155.90  
  Purchase #4 $86.37   10.266%   $95.2367   $95.24   $95.25   $95.20  
  Purchase #5 $40.37   10.379%   $44.56   $44.56   $44.55   $44.60  
  Purchase #6 $53.26   13.174%   $60.2765   $60.28   $60.30   $60.30  
  Purchase #7 $48.98   7.701%   $52.7519   $52.75   $52.75   $52.80  
  7 purchase totals = $860.11       $928.4138   $928.42   $928.50   $928.50