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 $184.90   8.163%   $199.9934   $199.99   $200.00   $200.00  
  Purchase #2 $122.79   12.152%   $137.7114   $137.71   $137.70   $137.70  
  Purchase #3 $217.66   11.645%   $243.0065   $243.01   $243.00   $243.00  
  Purchase #4 $225.58   10.847%   $250.0487   $250.05   $250.05   $250.00  
  Purchase #5 $54.94   10.292%   $60.5944   $60.59   $60.60   $60.60  
  Purchase #6 $33.64   5.763%   $35.5787   $35.58   $35.60   $35.60  
  Purchase #7 $74.35   13.459%   $84.3568   $84.36   $84.35   $84.40  
  7 purchase totals = $913.86       $1,011.2899   $1,011.29   $1,011.30   $1,011.30