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 $87.44   6.708%   $93.3055   $93.31   $93.30   $93.30  
  Purchase #2 $181.88   3.780%   $188.7551   $188.76   $188.75   $188.80  
  Purchase #3 $205.78   12.808%   $232.1363   $232.14   $232.15   $232.10  
  Purchase #4 $61.50   3.211%   $63.4748   $63.47   $63.45   $63.50  
  Purchase #5 $162.47   3.236%   $167.7275   $167.73   $167.75   $167.70  
  Purchase #6 $196.51   4.528%   $205.408   $205.41   $205.40   $205.40  
  Purchase #7 $207.62   4.390%   $216.7345   $216.73   $216.75   $216.70  
  7 purchase totals = $1,103.20       $1,167.5417   $1,167.55   $1,167.55   $1,167.50