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 $134.44   13.175%   $152.1525   $152.15   $152.15   $152.20  
  Purchase #2 $220.61   5.776%   $233.3524   $233.35   $233.35   $233.40  
  Purchase #3 $119.45   3.707%   $123.878   $123.88   $123.90   $123.90  
  Purchase #4 $198.28   6.339%   $210.849   $210.85   $210.85   $210.80  
  Purchase #5 $236.88   9.265%   $258.8269   $258.83   $258.85   $258.80  
  Purchase #6 $31.91   13.439%   $36.1984   $36.20   $36.20   $36.20  
  Purchase #7 $220.60   6.712%   $235.4067   $235.41   $235.40   $235.40  
  7 purchase totals = $1,162.17       $1,250.6639   $1,250.67   $1,250.70   $1,250.70