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 $241.45   3.520%   $249.949   $249.95   $249.95   $249.90  
  Purchase #2 $207.95   8.828%   $226.3078   $226.31   $226.30   $226.30  
  Purchase #3 $101.52   4.749%   $106.3412   $106.34   $106.35   $106.30  
  Purchase #4 $102.62   11.754%   $114.682   $114.68   $114.70   $114.70  
  Purchase #5 $31.94   6.433%   $33.9947   $33.99   $34.00   $34.00  
  Purchase #6 $196.28   6.389%   $208.8203   $208.82   $208.80   $208.80  
  Purchase #7 $87.27   7.694%   $93.9846   $93.98   $94.00   $94.00  
  7 purchase totals = $969.03       $1,034.0796   $1,034.07   $1,034.10   $1,034.00