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 $243.71   7.831%   $262.7949   $262.79   $262.80   $262.80  
  Purchase #2 $95.46   3.143%   $98.4603   $98.46   $98.45   $98.50  
  Purchase #3 $186.77   12.157%   $209.4756   $209.48   $209.50   $209.50  
  Purchase #4 $30.53   8.439%   $33.1064   $33.11   $33.10   $33.10  
  Purchase #5 $122.65   9.170%   $133.897   $133.90   $133.90   $133.90  
  Purchase #6 $246.25   3.191%   $254.1078   $254.11   $254.10   $254.10  
  Purchase #7 $60.48   4.729%   $63.3401   $63.34   $63.35   $63.30  
  7 purchase totals = $985.85       $1,055.1821   $1,055.19   $1,055.20   $1,055.20