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 $193.57   8.349%   $209.7312   $209.73   $209.75   $209.70  
  Purchase #2 $91.87   8.174%   $99.3795   $99.38   $99.40   $99.40  
  Purchase #3 $153.90   4.615%   $161.0025   $161.00   $161.00   $161.00  
  Purchase #4 $151.69   12.629%   $170.8469   $170.85   $170.85   $170.80  
  Purchase #5 $238.85   3.857%   $248.0624   $248.06   $248.05   $248.10  
  Purchase #6 $117.28   9.473%   $128.3899   $128.39   $128.40   $128.40  
  Purchase #7 $8.87   7.477%   $9.5332   $9.53   $9.55   $9.50  
  7 purchase totals = $956.03       $1,026.9456   $1,026.94   $1,027.00   $1,026.90