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 $114.41   11.683%   $127.7765   $127.78   $127.80   $127.80  
  Purchase #2 $54.91   12.174%   $61.5947   $61.59   $61.60   $61.60  
  Purchase #3 $116.65   4.746%   $122.1862   $122.19   $122.20   $122.20  
  Purchase #4 $13.98   13.225%   $15.8289   $15.83   $15.85   $15.80  
  Purchase #5 $115.49   3.569%   $119.6118   $119.61   $119.60   $119.60  
  Purchase #6 $167.84   4.199%   $174.8876   $174.89   $174.90   $174.90  
  Purchase #7 $170.67   6.147%   $181.1611   $181.16   $181.15   $181.20  
  7 purchase totals = $753.95       $803.0468   $803.05   $803.10   $803.10