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 $50.82   6.368%   $54.0562   $54.06   $54.05   $54.10  
  Purchase #2 $162.57   9.269%   $177.6386   $177.64   $177.65   $177.60  
  Purchase #3 $61.70   13.566%   $70.0702   $70.07   $70.05   $70.10  
  Purchase #4 $30.96   9.442%   $33.8832   $33.88   $33.90   $33.90  
  Purchase #5 $124.63   13.544%   $141.5099   $141.51   $141.50   $141.50  
  Purchase #6 $232.31   7.640%   $250.0585   $250.06   $250.05   $250.10  
  Purchase #7 $139.99   10.476%   $154.6554   $154.66   $154.65   $154.70  
  7 purchase totals = $802.98       $881.8720   $881.88   $881.85   $882.00