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 $83.88   3.437%   $86.763   $86.76   $86.75   $86.80  
  Purchase #2 $243.92   3.433%   $252.2938   $252.29   $252.30   $252.30  
  Purchase #3 $69.79   5.456%   $73.5977   $73.60   $73.60   $73.60  
  Purchase #4 $7.41   5.414%   $7.8112   $7.81   $7.80   $7.80  
  Purchase #5 $40.32   13.719%   $45.8515   $45.85   $45.85   $45.90  
  Purchase #6 $187.81   5.119%   $197.424   $197.42   $197.40   $197.40  
  Purchase #7 $92.70   5.817%   $98.0924   $98.09   $98.10   $98.10  
  7 purchase totals = $725.83       $761.8336   $761.82   $761.80   $761.90