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 $210.87   10.736%   $233.509   $233.51   $233.50   $233.50  
  Purchase #2 $39.31   10.453%   $43.4191   $43.42   $43.40   $43.40  
  Purchase #3 $202.92   4.633%   $212.3213   $212.32   $212.30   $212.30  
  Purchase #4 $27.81   11.243%   $30.9367   $30.94   $30.95   $30.90  
  Purchase #5 $101.25   13.829%   $115.2519   $115.25   $115.25   $115.30  
  Purchase #6 $22.86   6.426%   $24.329   $24.33   $24.35   $24.30  
  Purchase #7 $145.75   11.557%   $162.5943   $162.59   $162.60   $162.60  
  7 purchase totals = $750.77       $822.3613   $822.36   $822.35   $822.30