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 $52.36   5.861%   $55.4288   $55.43   $55.45   $55.40  
  Purchase #2 $188.36   10.813%   $208.7274   $208.73   $208.75   $208.70  
  Purchase #3 $21.37   12.294%   $23.9972   $24.00   $24.00   $24.00  
  Purchase #4 $54.69   11.422%   $60.9367   $60.94   $60.95   $60.90  
  Purchase #5 $207.36   12.334%   $232.9358   $232.94   $232.95   $232.90  
  Purchase #6 $102.82   3.112%   $106.0198   $106.02   $106.00   $106.00  
  Purchase #7 $93.54   3.145%   $96.4818   $96.48   $96.50   $96.50  
  7 purchase totals = $720.50       $784.5275   $784.54   $784.60   $784.40