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 $248.96   7.566%   $267.7963   $267.80   $267.80   $267.80  
  Purchase #2 $41.90   3.585%   $43.4021   $43.40   $43.40   $43.40  
  Purchase #3 $236.29   12.414%   $265.623   $265.62   $265.60   $265.60  
  Purchase #4 $110.87   6.479%   $118.0533   $118.05   $118.05   $118.10  
  Purchase #5 $227.96   6.466%   $242.6999   $242.70   $242.70   $242.70  
  Purchase #6 $45.49   8.191%   $49.2161   $49.22   $49.20   $49.20  
  Purchase #7 $23.85   9.453%   $26.1045   $26.10   $26.10   $26.10  
  7 purchase totals = $935.32       $1,012.8952   $1,012.89   $1,012.85   $1,012.90