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 $41.77   4.339%   $43.5824   $43.58   $43.60   $43.60  
  Purchase #2 $199.27   11.690%   $222.5647   $222.56   $222.55   $222.60  
  Purchase #3 $68.28   11.217%   $75.939   $75.94   $75.95   $75.90  
  Purchase #4 $128.42   8.230%   $138.989   $138.99   $139.00   $139.00  
  Purchase #5 $216.25   6.755%   $230.8577   $230.86   $230.85   $230.90  
  Purchase #6 $57.42   9.820%   $63.0586   $63.06   $63.05   $63.10  
  Purchase #7 $104.71   3.821%   $108.711   $108.71   $108.70   $108.70  
  7 purchase totals = $816.12       $883.7024   $883.70   $883.70   $883.80