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 $174.76   9.869%   $192.0071   $192.01   $192.00   $192.00  
  Purchase #2 $200.26   8.365%   $217.0117   $217.01   $217.00   $217.00  
  Purchase #3 $30.99   12.311%   $34.8052   $34.81   $34.80   $34.80  
  Purchase #4 $196.80   11.313%   $219.064   $219.06   $219.05   $219.10  
  Purchase #5 $172.76   9.256%   $188.7507   $188.75   $188.75   $188.80  
  Purchase #6 $27.27   3.678%   $28.273   $28.27   $28.25   $28.30  
  Purchase #7 $136.78   10.310%   $150.882   $150.88   $150.90   $150.90  
  7 purchase totals = $939.62       $1,030.7937   $1,030.79   $1,030.75   $1,030.90