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 $34.39   8.582%   $37.3413   $37.34   $37.35   $37.30  
  Purchase #2 $135.33   10.680%   $149.7832   $149.78   $149.80   $149.80  
  Purchase #3 $230.32   4.720%   $241.1911   $241.19   $241.20   $241.20  
  Purchase #4 $24.93   5.472%   $26.2942   $26.29   $26.30   $26.30  
  Purchase #5 $42.77   9.620%   $46.8845   $46.88   $46.90   $46.90  
  Purchase #6 $208.68   7.464%   $224.2559   $224.26   $224.25   $224.30  
  Purchase #7 $24.41   4.572%   $25.526   $25.53   $25.55   $25.50  
  7 purchase totals = $700.83       $751.2762   $751.27   $751.35   $751.30