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 $247.84   11.381%   $276.0467   $276.05   $276.05   $276.00  
  Purchase #2 $234.64   7.312%   $251.7969   $251.80   $251.80   $251.80  
  Purchase #3 $82.98   3.679%   $86.0328   $86.03   $86.05   $86.00  
  Purchase #4 $95.89   5.408%   $101.0757   $101.08   $101.10   $101.10  
  Purchase #5 $243.89   3.832%   $253.2359   $253.24   $253.25   $253.20  
  Purchase #6 $86.50   6.276%   $91.9287   $91.93   $91.95   $91.90  
  Purchase #7 $48.51   9.315%   $53.0287   $53.03   $53.05   $53.00  
  7 purchase totals = $1,040.25       $1,113.1454   $1,113.16   $1,113.25   $1,113.00