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 $53.60   13.428%   $60.7974   $60.80   $60.80   $60.80  
  Purchase #2 $201.63   8.784%   $219.3412   $219.34   $219.35   $219.30  
  Purchase #3 $174.45   9.777%   $191.506   $191.51   $191.50   $191.50  
  Purchase #4 $224.30   13.212%   $253.9345   $253.93   $253.95   $253.90  
  Purchase #5 $166.73   6.775%   $178.026   $178.03   $178.05   $178.00  
  Purchase #6 $25.51   6.661%   $27.2092   $27.21   $27.20   $27.20  
  Purchase #7 $32.79   9.126%   $35.7824   $35.78   $35.80   $35.80  
  7 purchase totals = $879.01       $966.5967   $966.60   $966.65   $966.50