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 $68.29   13.265%   $77.3487   $77.35   $77.35   $77.30  
  Purchase #2 $231.76   12.221%   $260.0834   $260.08   $260.10   $260.10  
  Purchase #3 $141.99   11.263%   $157.9823   $157.98   $158.00   $158.00  
  Purchase #4 $44.70   13.800%   $50.8686   $50.87   $50.85   $50.90  
  Purchase #5 $41.29   6.568%   $44.0019   $44.00   $44.00   $44.00  
  Purchase #6 $214.30   4.283%   $223.4785   $223.48   $223.50   $223.50  
  Purchase #7 $201.71   8.546%   $218.9481   $218.95   $218.95   $218.90  
  7 purchase totals = $944.04       $1,032.7115   $1,032.71   $1,032.75   $1,032.70