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 $184.85   9.266%   $201.9782   $201.98   $202.00   $202.00  
  Purchase #2 $63.80   10.217%   $70.3184   $70.32   $70.30   $70.30  
  Purchase #3 $24.37   7.649%   $26.2341   $26.23   $26.25   $26.20  
  Purchase #4 $250.42   10.606%   $276.9795   $276.98   $277.00   $277.00  
  Purchase #5 $101.90   5.435%   $107.4383   $107.44   $107.45   $107.40  
  Purchase #6 $220.87   4.365%   $230.511   $230.51   $230.50   $230.50  
  Purchase #7 $123.62   7.599%   $133.0139   $133.01   $133.00   $133.00  
  7 purchase totals = $969.83       $1,046.4734   $1,046.47   $1,046.50   $1,046.40