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 $73.81   4.813%   $77.3625   $77.36   $77.35   $77.40  
  Purchase #2 $206.87   12.611%   $232.9584   $232.96   $232.95   $233.00  
  Purchase #3 $187.27   8.122%   $202.4801   $202.48   $202.50   $202.50  
  Purchase #4 $245.81   11.632%   $274.4026   $274.40   $274.40   $274.40  
  Purchase #5 $74.78   5.365%   $78.7919   $78.79   $78.80   $78.80  
  Purchase #6 $206.51   6.691%   $220.3276   $220.33   $220.35   $220.30  
  Purchase #7 $159.70   4.730%   $167.2538   $167.25   $167.25   $167.30  
  7 purchase totals = $1,154.75       $1,253.5769   $1,253.57   $1,253.60   $1,253.70