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 $24.53   7.842%   $26.4536   $26.45   $26.45   $26.50  
  Purchase #2 $165.56   5.554%   $174.7552   $174.76   $174.75   $174.80  
  Purchase #3 $45.34   3.631%   $46.9863   $46.99   $47.00   $47.00  
  Purchase #4 $166.90   8.383%   $180.8912   $180.89   $180.90   $180.90  
  Purchase #5 $170.88   7.451%   $183.6123   $183.61   $183.60   $183.60  
  Purchase #6 $228.92   9.293%   $250.1935   $250.19   $250.20   $250.20  
  Purchase #7 $202.96   5.809%   $214.7499   $214.75   $214.75   $214.70  
  7 purchase totals = $1,005.09       $1,077.6420   $1,077.64   $1,077.65   $1,077.70