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 $24.48   9.759%   $26.869   $26.87   $26.85   $26.90  
  Purchase #2 $135.38   8.537%   $146.9374   $146.94   $146.95   $146.90  
  Purchase #3 $168.30   11.433%   $187.5417   $187.54   $187.55   $187.50  
  Purchase #4 $213.92   13.802%   $243.4452   $243.45   $243.45   $243.40  
  Purchase #5 $28.70   9.133%   $31.3212   $31.32   $31.30   $31.30  
  Purchase #6 $169.77   11.188%   $188.7639   $188.76   $188.75   $188.80  
  Purchase #7 $229.58   4.550%   $240.0259   $240.03   $240.05   $240.00  
  7 purchase totals = $970.13       $1,064.9043   $1,064.91   $1,064.90   $1,064.80