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 $197.25   6.290%   $209.657   $209.66   $209.65   $209.70  
  Purchase #2 $93.91   11.717%   $104.9134   $104.91   $104.90   $104.90  
  Purchase #3 $110.32   7.176%   $118.2366   $118.24   $118.25   $118.20  
  Purchase #4 $148.66   11.581%   $165.8763   $165.88   $165.90   $165.90  
  Purchase #5 $173.68   10.295%   $191.5604   $191.56   $191.55   $191.60  
  Purchase #6 $250.90   6.348%   $266.8271   $266.83   $266.85   $266.80  
  Purchase #7 $106.77   5.547%   $112.6925   $112.69   $112.70   $112.70  
  7 purchase totals = $1,081.49       $1,169.7633   $1,169.77   $1,169.80   $1,169.80