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 $217.53   10.844%   $241.119   $241.12   $241.10   $241.10  
  Purchase #2 $49.72   8.449%   $53.9208   $53.92   $53.90   $53.90  
  Purchase #3 $167.69   4.252%   $174.8202   $174.82   $174.80   $174.80  
  Purchase #4 $89.49   7.790%   $96.4613   $96.46   $96.45   $96.50  
  Purchase #5 $143.63   11.169%   $159.672   $159.67   $159.65   $159.70  
  Purchase #6 $48.33   12.154%   $54.204   $54.20   $54.20   $54.20  
  Purchase #7 $74.81   12.573%   $84.2159   $84.22   $84.20   $84.20  
  7 purchase totals = $791.20       $864.4132   $864.41   $864.30   $864.40