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 $101.69   11.236%   $113.1159   $113.12   $113.10   $113.10  
  Purchase #2 $196.41   10.839%   $217.6989   $217.70   $217.70   $217.70  
  Purchase #3 $17.47   10.471%   $19.2993   $19.30   $19.30   $19.30  
  Purchase #4 $242.71   6.589%   $258.7022   $258.70   $258.70   $258.70  
  Purchase #5 $23.48   13.452%   $26.6385   $26.64   $26.65   $26.60  
  Purchase #6 $168.56   9.591%   $184.7266   $184.73   $184.75   $184.70  
  Purchase #7 $191.42   13.670%   $217.5871   $217.59   $217.60   $217.60  
  7 purchase totals = $941.74       $1,037.7685   $1,037.78   $1,037.80   $1,037.70