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 $61.98   3.293%   $64.021   $64.02   $64.00   $64.00  
  Purchase #2 $218.43   4.395%   $228.03   $228.03   $228.05   $228.00  
  Purchase #3 $42.50   5.746%   $44.9421   $44.94   $44.95   $44.90  
  Purchase #4 $167.43   12.258%   $187.9536   $187.95   $187.95   $188.00  
  Purchase #5 $231.65   8.723%   $251.8568   $251.86   $251.85   $251.90  
  Purchase #6 $62.64   11.384%   $69.7709   $69.77   $69.75   $69.80  
  Purchase #7 $229.30   5.199%   $241.2213   $241.22   $241.20   $241.20  
  7 purchase totals = $1,013.93       $1,087.7957   $1,087.79   $1,087.75   $1,087.80