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 $245.58   11.835%   $274.6444   $274.64   $274.65   $274.60  
  Purchase #2 $21.91   12.389%   $24.6244   $24.62   $24.60   $24.60  
  Purchase #3 $146.60   8.146%   $158.542   $158.54   $158.55   $158.50  
  Purchase #4 $77.66   12.143%   $87.0903   $87.09   $87.10   $87.10  
  Purchase #5 $240.35   12.163%   $269.5838   $269.58   $269.60   $269.60  
  Purchase #6 $114.39   12.196%   $128.341   $128.34   $128.35   $128.30  
  Purchase #7 $231.82   8.268%   $250.9869   $250.99   $251.00   $251.00  
  7 purchase totals = $1,078.31       $1,193.8128   $1,193.80   $1,193.85   $1,193.70