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 $184.86   11.864%   $206.7918   $206.79   $206.80   $206.80  
  Purchase #2 $169.48   11.138%   $188.3567   $188.36   $188.35   $188.40  
  Purchase #3 $155.29   7.423%   $166.8172   $166.82   $166.80   $166.80  
  Purchase #4 $61.50   7.272%   $65.9723   $65.97   $65.95   $66.00  
  Purchase #5 $214.26   10.231%   $236.1809   $236.18   $236.20   $236.20  
  Purchase #6 $28.83   3.643%   $29.8803   $29.88   $29.90   $29.90  
  Purchase #7 $182.54   7.736%   $196.6613   $196.66   $196.65   $196.70  
  7 purchase totals = $996.76       $1,090.6605   $1,090.66   $1,090.65   $1,090.80