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 $184.48   12.782%   $208.0602   $208.06   $208.05   $208.10  
  Purchase #2 $213.45   8.690%   $231.9988   $232.00   $232.00   $232.00  
  Purchase #3 $95.60   11.529%   $106.6217   $106.62   $106.60   $106.60  
  Purchase #4 $56.72   11.197%   $63.0709   $63.07   $63.05   $63.10  
  Purchase #5 $11.54   3.809%   $11.9796   $11.98   $12.00   $12.00  
  Purchase #6 $225.31   5.535%   $237.7809   $237.78   $237.80   $237.80  
  Purchase #7 $228.87   9.291%   $250.1343   $250.13   $250.15   $250.10  
  7 purchase totals = $1,015.97       $1,109.6464   $1,109.64   $1,109.65   $1,109.70