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 $196.33   8.337%   $212.698   $212.70   $212.70   $212.70  
  Purchase #2 $52.38   12.135%   $58.7363   $58.74   $58.75   $58.70  
  Purchase #3 $249.84   12.591%   $281.2974   $281.30   $281.30   $281.30  
  Purchase #4 $50.38   11.505%   $56.1762   $56.18   $56.20   $56.20  
  Purchase #5 $129.92   13.131%   $146.9798   $146.98   $147.00   $147.00  
  Purchase #6 $167.38   10.643%   $185.1943   $185.19   $185.20   $185.20  
  Purchase #7 $73.82   3.245%   $76.2155   $76.22   $76.20   $76.20  
  7 purchase totals = $920.05       $1,017.2975   $1,017.31   $1,017.35   $1,017.30