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 $226.95   6.589%   $241.9037   $241.90   $241.90   $241.90  
  Purchase #2 $35.75   11.152%   $39.7368   $39.74   $39.75   $39.70  
  Purchase #3 $66.80   4.829%   $70.0258   $70.03   $70.05   $70.00  
  Purchase #4 $186.78   8.468%   $202.5965   $202.60   $202.60   $202.60  
  Purchase #5 $148.89   13.180%   $168.5137   $168.51   $168.50   $168.50  
  Purchase #6 $36.66   5.802%   $38.787   $38.79   $38.80   $38.80  
  Purchase #7 $235.49   11.810%   $263.3014   $263.30   $263.30   $263.30  
  7 purchase totals = $937.32       $1,024.8649   $1,024.87   $1,024.90   $1,024.80