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 $246.40   8.632%   $267.6692   $267.67   $267.65   $267.70  
  Purchase #2 $180.44   12.773%   $203.4876   $203.49   $203.50   $203.50  
  Purchase #3 $30.56   6.791%   $32.6353   $32.64   $32.65   $32.60  
  Purchase #4 $73.65   10.674%   $81.5114   $81.51   $81.50   $81.50  
  Purchase #5 $223.38   8.272%   $241.858   $241.86   $241.85   $241.90  
  Purchase #6 $84.67   13.253%   $95.8913   $95.89   $95.90   $95.90  
  Purchase #7 $64.87   4.859%   $68.022   $68.02   $68.00   $68.00  
  7 purchase totals = $903.97       $991.0748   $991.08   $991.05   $991.10