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 $175.64   11.779%   $196.3286   $196.33   $196.35   $196.30  
  Purchase #2 $91.50   5.644%   $96.6643   $96.66   $96.65   $96.70  
  Purchase #3 $241.84   13.292%   $273.9854   $273.99   $274.00   $274.00  
  Purchase #4 $127.72   13.310%   $144.7195   $144.72   $144.70   $144.70  
  Purchase #5 $149.26   11.186%   $165.9562   $165.96   $165.95   $166.00  
  Purchase #6 $71.94   13.660%   $81.767   $81.77   $81.75   $81.80  
  Purchase #7 $114.90   9.496%   $125.8109   $125.81   $125.80   $125.80  
  7 purchase totals = $972.80       $1,085.2319   $1,085.24   $1,085.20   $1,085.30