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 $123.67   8.741%   $134.48   $134.48   $134.50   $134.50  
  Purchase #2 $39.61   13.241%   $44.8548   $44.85   $44.85   $44.90  
  Purchase #3 $197.83   13.209%   $223.9614   $223.96   $223.95   $224.00  
  Purchase #4 $89.95   4.252%   $93.7747   $93.77   $93.75   $93.80  
  Purchase #5 $149.53   6.495%   $159.242   $159.24   $159.25   $159.20  
  Purchase #6 $120.38   6.525%   $128.2348   $128.23   $128.25   $128.20  
  Purchase #7 $228.92   5.485%   $241.4763   $241.48   $241.50   $241.50  
  7 purchase totals = $949.89       $1,026.0240   $1,026.01   $1,026.05   $1,026.10