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 $208.43   6.104%   $221.1526   $221.15   $221.15   $221.20  
  Purchase #2 $108.67   11.199%   $120.84   $120.84   $120.85   $120.80  
  Purchase #3 $81.57   6.429%   $86.8141   $86.81   $86.80   $86.80  
  Purchase #4 $244.87   5.225%   $257.6645   $257.66   $257.65   $257.70  
  Purchase #5 $98.69   7.560%   $106.151   $106.15   $106.15   $106.20  
  Purchase #6 $157.55   13.743%   $179.2021   $179.20   $179.20   $179.20  
  Purchase #7 $94.71   7.317%   $101.6399   $101.64   $101.65   $101.60  
  7 purchase totals = $994.49       $1,073.4642   $1,073.45   $1,073.45   $1,073.50