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 $222.27   11.740%   $248.3645   $248.36   $248.35   $248.40  
  Purchase #2 $120.44   9.286%   $131.6241   $131.62   $131.60   $131.60  
  Purchase #3 $69.83   7.220%   $74.8717   $74.87   $74.85   $74.90  
  Purchase #4 $53.86   3.290%   $55.632   $55.63   $55.65   $55.60  
  Purchase #5 $181.69   7.274%   $194.9061   $194.91   $194.90   $194.90  
  Purchase #6 $103.43   4.535%   $108.1206   $108.12   $108.10   $108.10  
  Purchase #7 $113.56   6.856%   $121.3457   $121.35   $121.35   $121.30  
  7 purchase totals = $865.08       $934.8647   $934.86   $934.80   $934.80