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 $184.64   11.435%   $205.7536   $205.75   $205.75   $205.80  
  Purchase #2 $226.48   8.456%   $245.6311   $245.63   $245.65   $245.60  
  Purchase #3 $165.98   6.488%   $176.7488   $176.75   $176.75   $176.70  
  Purchase #4 $139.38   4.728%   $145.9699   $145.97   $145.95   $146.00  
  Purchase #5 $138.41   6.430%   $147.3098   $147.31   $147.30   $147.30  
  Purchase #6 $147.86   6.528%   $157.5123   $157.51   $157.50   $157.50  
  Purchase #7 $191.31   3.441%   $197.893   $197.89   $197.90   $197.90  
  7 purchase totals = $1,194.06       $1,276.8185   $1,276.81   $1,276.80   $1,276.80