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 $167.66   11.157%   $186.3658   $186.37   $186.35   $186.40  
  Purchase #2 $246.35   10.779%   $272.9041   $272.90   $272.90   $272.90  
  Purchase #3 $216.96   10.473%   $239.6822   $239.68   $239.70   $239.70  
  Purchase #4 $150.67   5.811%   $159.4254   $159.43   $159.45   $159.40  
  Purchase #5 $95.63   3.140%   $98.6328   $98.63   $98.65   $98.60  
  Purchase #6 $87.46   6.197%   $92.8799   $92.88   $92.90   $92.90  
  Purchase #7 $191.35   3.172%   $197.4196   $197.42   $197.40   $197.40  
  7 purchase totals = $1,156.08       $1,247.3098   $1,247.31   $1,247.35   $1,247.30