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 $94.81   7.210%   $101.6458   $101.65   $101.65   $101.60  
  Purchase #2 $36.41   5.319%   $38.3466   $38.35   $38.35   $38.30  
  Purchase #3 $26.51   10.337%   $29.2503   $29.25   $29.25   $29.30  
  Purchase #4 $58.79   9.655%   $64.4662   $64.47   $64.45   $64.50  
  Purchase #5 $218.91   3.635%   $226.8674   $226.87   $226.85   $226.90  
  Purchase #6 $69.37   8.148%   $75.0223   $75.02   $75.00   $75.00  
  Purchase #7 $20.37   11.704%   $22.7541   $22.75   $22.75   $22.80  
  7 purchase totals = $525.17       $558.3527   $558.36   $558.30   $558.40