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 $227.68   11.393%   $253.6196   $253.62   $253.60   $253.60  
  Purchase #2 $160.51   4.206%   $167.2611   $167.26   $167.25   $167.30  
  Purchase #3 $233.75   5.193%   $245.8886   $245.89   $245.90   $245.90  
  Purchase #4 $170.37   8.375%   $184.6385   $184.64   $184.65   $184.60  
  Purchase #5 $66.50   12.662%   $74.9202   $74.92   $74.90   $74.90  
  Purchase #6 $59.88   6.125%   $63.5477   $63.55   $63.55   $63.50  
  Purchase #7 $204.68   3.689%   $212.2306   $212.23   $212.25   $212.20  
  7 purchase totals = $1,123.37       $1,202.1063   $1,202.11   $1,202.10   $1,202.00