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 $86.42   9.476%   $94.6092   $94.61   $94.60   $94.60  
  Purchase #2 $62.85   13.217%   $71.1569   $71.16   $71.15   $71.20  
  Purchase #3 $154.78   5.742%   $163.6675   $163.67   $163.65   $163.70  
  Purchase #4 $67.51   11.789%   $75.4688   $75.47   $75.45   $75.50  
  Purchase #5 $15.29   6.576%   $16.2955   $16.30   $16.30   $16.30  
  Purchase #6 $79.57   4.482%   $83.1363   $83.14   $83.15   $83.10  
  Purchase #7 $54.46   13.335%   $61.7222   $61.72   $61.70   $61.70  
  7 purchase totals = $520.88       $566.0564   $566.07   $566.00   $566.10