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 $55.92   4.619%   $58.5029   $58.50   $58.50   $58.50  
  Purchase #2 $186.73   9.575%   $204.6094   $204.61   $204.60   $204.60  
  Purchase #3 $245.34   6.336%   $260.8847   $260.88   $260.90   $260.90  
  Purchase #4 $127.99   9.420%   $140.0467   $140.05   $140.05   $140.00  
  Purchase #5 $160.80   11.690%   $179.5975   $179.60   $179.60   $179.60  
  Purchase #6 $44.39   9.449%   $48.5844   $48.58   $48.60   $48.60  
  Purchase #7 $171.27   7.712%   $184.4783   $184.48   $184.50   $184.50  
  7 purchase totals = $992.44       $1,076.7039   $1,076.70   $1,076.75   $1,076.70