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 $189.44   9.275%   $207.0106   $207.01   $207.00   $207.00  
  Purchase #2 $223.37   10.497%   $246.8171   $246.82   $246.80   $246.80  
  Purchase #3 $207.95   3.271%   $214.752   $214.75   $214.75   $214.80  
  Purchase #4 $41.45   9.577%   $45.4197   $45.42   $45.40   $45.40  
  Purchase #5 $12.29   5.567%   $12.9742   $12.97   $12.95   $13.00  
  Purchase #6 $208.93   5.543%   $220.511   $220.51   $220.50   $220.50  
  Purchase #7 $79.85   3.484%   $82.632   $82.63   $82.65   $82.60  
  7 purchase totals = $963.28       $1,030.1166   $1,030.11   $1,030.05   $1,030.10