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 $228.36   11.352%   $254.2834   $254.28   $254.30   $254.30  
  Purchase #2 $192.42   9.849%   $211.3714   $211.37   $211.35   $211.40  
  Purchase #3 $33.98   3.539%   $35.1826   $35.18   $35.20   $35.20  
  Purchase #4 $86.44   11.390%   $96.2855   $96.29   $96.30   $96.30  
  Purchase #5 $190.70   10.507%   $210.7368   $210.74   $210.75   $210.70  
  Purchase #6 $166.44   8.146%   $179.9982   $180.00   $180.00   $180.00  
  Purchase #7 $232.95   12.788%   $262.7396   $262.74   $262.75   $262.70  
  7 purchase totals = $1,131.29       $1,250.5975   $1,250.60   $1,250.65   $1,250.60