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 $42.30   5.618%   $44.6764   $44.68   $44.70   $44.70  
  Purchase #2 $187.60   12.773%   $211.5621   $211.56   $211.55   $211.60  
  Purchase #3 $134.82   7.167%   $144.4825   $144.48   $144.50   $144.50  
  Purchase #4 $235.35   5.663%   $248.6779   $248.68   $248.70   $248.70  
  Purchase #5 $33.67   10.648%   $37.2552   $37.26   $37.25   $37.30  
  Purchase #6 $167.69   6.283%   $178.226   $178.23   $178.25   $178.20  
  Purchase #7 $191.65   10.216%   $211.229   $211.23   $211.25   $211.20  
  7 purchase totals = $993.08       $1,076.1091   $1,076.12   $1,076.20   $1,076.20