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 $233.27   7.410%   $250.5553   $250.56   $250.55   $250.60  
  Purchase #2 $23.54   13.384%   $26.6906   $26.69   $26.70   $26.70  
  Purchase #3 $144.32   11.528%   $160.9572   $160.96   $160.95   $161.00  
  Purchase #4 $156.47   13.519%   $177.6232   $177.62   $177.60   $177.60  
  Purchase #5 $225.88   9.735%   $247.8694   $247.87   $247.85   $247.90  
  Purchase #6 $157.90   13.272%   $178.8565   $178.86   $178.85   $178.90  
  Purchase #7 $134.50   11.219%   $149.5896   $149.59   $149.60   $149.60  
  7 purchase totals = $1,075.88       $1,192.1418   $1,192.15   $1,192.10   $1,192.30