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 $88.96   6.718%   $94.9363   $94.94   $94.95   $94.90  
  Purchase #2 $59.74   4.505%   $62.4313   $62.43   $62.45   $62.40  
  Purchase #3 $163.54   6.731%   $174.5479   $174.55   $174.55   $174.50  
  Purchase #4 $44.76   5.183%   $47.0799   $47.08   $47.10   $47.10  
  Purchase #5 $110.80   5.388%   $116.7699   $116.77   $116.75   $116.80  
  Purchase #6 $77.27   12.469%   $86.9048   $86.90   $86.90   $86.90  
  Purchase #7 $16.92   13.394%   $19.1863   $19.19   $19.20   $19.20  
  7 purchase totals = $561.99       $601.8564   $601.86   $601.90   $601.80