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 $137.93   3.365%   $142.5713   $142.57   $142.55   $142.60  
  Purchase #2 $198.62   13.406%   $225.247   $225.25   $225.25   $225.20  
  Purchase #3 $196.82   7.517%   $211.615   $211.62   $211.60   $211.60  
  Purchase #4 $202.54   5.687%   $214.0584   $214.06   $214.05   $214.10  
  Purchase #5 $91.53   5.324%   $96.4031   $96.40   $96.40   $96.40  
  Purchase #6 $221.26   3.199%   $228.3381   $228.34   $228.35   $228.30  
  Purchase #7 $244.59   7.671%   $263.3525   $263.35   $263.35   $263.40  
  7 purchase totals = $1,293.29       $1,381.5854   $1,381.59   $1,381.55   $1,381.60