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 $94.37   13.409%   $107.0241   $107.02   $107.00   $107.00  
  Purchase #2 $189.63   9.716%   $208.0545   $208.05   $208.05   $208.10  
  Purchase #3 $202.52   12.438%   $227.7094   $227.71   $227.70   $227.70  
  Purchase #4 $49.54   13.775%   $56.3641   $56.36   $56.35   $56.40  
  Purchase #5 $246.73   11.106%   $274.1318   $274.13   $274.15   $274.10  
  Purchase #6 $101.98   9.834%   $112.0087   $112.01   $112.00   $112.00  
  Purchase #7 $25.48   3.408%   $26.3484   $26.35   $26.35   $26.30  
  7 purchase totals = $910.25       $1,011.6410   $1,011.63   $1,011.60   $1,011.60