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 $232.78   3.790%   $241.6024   $241.60   $241.60   $241.60  
  Purchase #2 $177.73   10.620%   $196.6049   $196.60   $196.60   $196.60  
  Purchase #3 $8.44   9.505%   $9.2422   $9.24   $9.25   $9.20  
  Purchase #4 $5.93   6.314%   $6.3044   $6.30   $6.30   $6.30  
  Purchase #5 $30.42   7.272%   $32.6321   $32.63   $32.65   $32.60  
  Purchase #6 $203.91   11.317%   $226.9865   $226.99   $227.00   $227.00  
  Purchase #7 $83.75   4.589%   $87.5933   $87.59   $87.60   $87.60  
  7 purchase totals = $742.96       $800.9658   $800.95   $801.00   $800.90