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 $113.49   9.514%   $124.2874   $124.29   $124.30   $124.30  
  Purchase #2 $59.88   9.501%   $65.5692   $65.57   $65.55   $65.60  
  Purchase #3 $167.93   3.706%   $174.1535   $174.15   $174.15   $174.20  
  Purchase #4 $85.72   10.368%   $94.6074   $94.61   $94.60   $94.60  
  Purchase #5 $175.28   10.610%   $193.8772   $193.88   $193.90   $193.90  
  Purchase #6 $212.75   6.421%   $226.4107   $226.41   $226.40   $226.40  
  Purchase #7 $241.38   4.627%   $252.5487   $252.55   $252.55   $252.50  
  7 purchase totals = $1,056.43       $1,131.4541   $1,131.46   $1,131.45   $1,131.50