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 $58.36   6.457%   $62.1283   $62.13   $62.15   $62.10  
  Purchase #2 $211.78   4.742%   $221.8226   $221.82   $221.80   $221.80  
  Purchase #3 $228.35   6.145%   $242.3821   $242.38   $242.40   $242.40  
  Purchase #4 $96.61   5.235%   $101.6675   $101.67   $101.65   $101.70  
  Purchase #5 $13.95   3.199%   $14.3963   $14.40   $14.40   $14.40  
  Purchase #6 $210.83   7.608%   $226.8699   $226.87   $226.85   $226.90  
  Purchase #7 $30.65   6.342%   $32.5938   $32.59   $32.60   $32.60  
  7 purchase totals = $850.53       $901.8605   $901.86   $901.85   $901.90