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 $86.28   12.247%   $96.8467   $96.85   $96.85   $96.80  
  Purchase #2 $189.59   7.707%   $204.2017   $204.20   $204.20   $204.20  
  Purchase #3 $250.49   13.732%   $284.8873   $284.89   $284.90   $284.90  
  Purchase #4 $26.97   8.760%   $29.3326   $29.33   $29.35   $29.30  
  Purchase #5 $136.81   11.256%   $152.2093   $152.21   $152.20   $152.20  
  Purchase #6 $79.92   9.302%   $87.3542   $87.35   $87.35   $87.40  
  Purchase #7 $222.44   13.303%   $252.0312   $252.03   $252.05   $252.00  
  7 purchase totals = $992.50       $1,106.8630   $1,106.86   $1,106.90   $1,106.80