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 $24.77   8.275%   $26.8197   $26.82   $26.80   $26.80  
  Purchase #2 $118.25   11.437%   $131.7743   $131.77   $131.75   $131.80  
  Purchase #3 $104.79   3.150%   $108.0909   $108.09   $108.10   $108.10  
  Purchase #4 $141.61   3.851%   $147.0634   $147.06   $147.05   $147.10  
  Purchase #5 $159.61   4.830%   $167.3192   $167.32   $167.30   $167.30  
  Purchase #6 $207.84   6.265%   $220.8612   $220.86   $220.85   $220.90  
  Purchase #7 $193.63   5.688%   $204.6437   $204.64   $204.65   $204.60  
  7 purchase totals = $950.50       $1,006.5724   $1,006.56   $1,006.50   $1,006.60