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 $246.62   6.584%   $262.8575   $262.86   $262.85   $262.90  
  Purchase #2 $29.67   5.720%   $31.3671   $31.37   $31.35   $31.40  
  Purchase #3 $141.99   9.847%   $155.9718   $155.97   $155.95   $156.00  
  Purchase #4 $53.55   12.869%   $60.4413   $60.44   $60.45   $60.40  
  Purchase #5 $80.80   5.203%   $85.004   $85.00   $85.00   $85.00  
  Purchase #6 $209.85   12.808%   $236.7276   $236.73   $236.75   $236.70  
  Purchase #7 $119.31   13.661%   $135.6089   $135.61   $135.60   $135.60  
  7 purchase totals = $881.79       $967.9782   $967.98   $967.95   $968.00