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 $232.80   12.629%   $262.2003   $262.20   $262.20   $262.20  
  Purchase #2 $141.47   4.567%   $147.9309   $147.93   $147.95   $147.90  
  Purchase #3 $84.27   5.757%   $89.1214   $89.12   $89.10   $89.10  
  Purchase #4 $188.61   6.811%   $201.4562   $201.46   $201.45   $201.50  
  Purchase #5 $196.95   6.644%   $210.0354   $210.04   $210.05   $210.00  
  Purchase #6 $237.70   9.508%   $260.3005   $260.30   $260.30   $260.30  
  Purchase #7 $191.91   6.141%   $203.6952   $203.70   $203.70   $203.70  
  7 purchase totals = $1,273.71       $1,374.7399   $1,374.75   $1,374.75   $1,374.70