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 $187.46   8.424%   $203.2516   $203.25   $203.25   $203.30  
  Purchase #2 $52.70   7.570%   $56.6894   $56.69   $56.70   $56.70  
  Purchase #3 $248.89   8.767%   $270.7102   $270.71   $270.70   $270.70  
  Purchase #4 $163.62   10.600%   $180.9637   $180.96   $180.95   $181.00  
  Purchase #5 $199.69   10.103%   $219.8647   $219.86   $219.85   $219.90  
  Purchase #6 $28.30   9.228%   $30.9115   $30.91   $30.90   $30.90  
  Purchase #7 $41.25   10.763%   $45.6897   $45.69   $45.70   $45.70  
  7 purchase totals = $921.91       $1,008.0808   $1,008.07   $1,008.05   $1,008.20