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 $67.66   4.263%   $70.5443   $70.54   $70.55   $70.50  
  Purchase #2 $156.47   5.613%   $165.2527   $165.25   $165.25   $165.30  
  Purchase #3 $212.60   11.862%   $237.8186   $237.82   $237.80   $237.80  
  Purchase #4 $161.95   4.189%   $168.7341   $168.73   $168.75   $168.70  
  Purchase #5 $79.84   5.466%   $84.2041   $84.20   $84.20   $84.20  
  Purchase #6 $148.40   12.730%   $167.2913   $167.29   $167.30   $167.30  
  Purchase #7 $128.45   3.159%   $132.5077   $132.51   $132.50   $132.50  
  7 purchase totals = $955.37       $1,026.3528   $1,026.34   $1,026.35   $1,026.30