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 $76.92   11.792%   $85.9904   $85.99   $86.00   $86.00  
  Purchase #2 $9.55   9.455%   $10.453   $10.45   $10.45   $10.50  
  Purchase #3 $86.81   12.743%   $97.8722   $97.87   $97.85   $97.90  
  Purchase #4 $240.60   7.505%   $258.657   $258.66   $258.65   $258.70  
  Purchase #5 $53.30   4.670%   $55.7891   $55.79   $55.80   $55.80  
  Purchase #6 $21.74   3.293%   $22.4559   $22.46   $22.45   $22.50  
  Purchase #7 $168.68   3.328%   $174.2937   $174.29   $174.30   $174.30  
  7 purchase totals = $657.60       $705.5113   $705.51   $705.50   $705.70