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 $231.27   11.822%   $258.6107   $258.61   $258.60   $258.60  
  Purchase #2 $219.44   7.283%   $235.4218   $235.42   $235.40   $235.40  
  Purchase #3 $238.76   7.573%   $256.8413   $256.84   $256.85   $256.80  
  Purchase #4 $63.59   12.432%   $71.4955   $71.50   $71.50   $71.50  
  Purchase #5 $99.98   6.543%   $106.5217   $106.52   $106.50   $106.50  
  Purchase #6 $235.87   11.227%   $262.3511   $262.35   $262.35   $262.40  
  Purchase #7 $119.55   4.533%   $124.9692   $124.97   $124.95   $125.00  
  7 purchase totals = $1,208.46       $1,316.2113   $1,316.21   $1,316.15   $1,316.20