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 $182.92   11.271%   $203.5369   $203.54   $203.55   $203.50  
  Purchase #2 $163.60   11.514%   $182.4369   $182.44   $182.45   $182.40  
  Purchase #3 $25.56   3.329%   $26.4109   $26.41   $26.40   $26.40  
  Purchase #4 $18.99   7.687%   $20.4498   $20.45   $20.45   $20.40  
  Purchase #5 $72.92   10.635%   $80.675   $80.68   $80.70   $80.70  
  Purchase #6 $246.84   3.170%   $254.6648   $254.66   $254.65   $254.70  
  Purchase #7 $222.78   8.753%   $242.2799   $242.28   $242.30   $242.30  
  7 purchase totals = $933.61       $1,010.4542   $1,010.46   $1,010.50   $1,010.40