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 $68.94   11.601%   $76.9377   $76.94   $76.95   $76.90  
  Purchase #2 $48.98   12.325%   $55.0168   $55.02   $55.00   $55.00  
  Purchase #3 $132.94   3.666%   $137.8136   $137.81   $137.80   $137.80  
  Purchase #4 $185.61   7.800%   $200.0876   $200.09   $200.10   $200.10  
  Purchase #5 $243.76   4.530%   $254.8023   $254.80   $254.80   $254.80  
  Purchase #6 $60.68   10.375%   $66.9756   $66.98   $67.00   $67.00  
  Purchase #7 $236.93   9.786%   $260.116   $260.12   $260.10   $260.10  
  7 purchase totals = $977.84       $1,051.7496   $1,051.76   $1,051.75   $1,051.70