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 $189.89   9.408%   $207.7549   $207.75   $207.75   $207.80  
  Purchase #2 $39.48   5.322%   $41.5811   $41.58   $41.60   $41.60  
  Purchase #3 $187.36   3.854%   $194.5809   $194.58   $194.60   $194.60  
  Purchase #4 $176.94   9.718%   $194.135   $194.14   $194.15   $194.10  
  Purchase #5 $149.75   8.561%   $162.5701   $162.57   $162.55   $162.60  
  Purchase #6 $30.99   6.551%   $33.0202   $33.02   $33.00   $33.00  
  Purchase #7 $222.83   3.271%   $230.1188   $230.12   $230.10   $230.10  
  7 purchase totals = $997.24       $1,063.7610   $1,063.76   $1,063.75   $1,063.80