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 $75.70   13.586%   $85.9846   $85.98   $86.00   $86.00  
  Purchase #2 $98.29   5.670%   $103.863   $103.86   $103.85   $103.90  
  Purchase #3 $202.52   10.762%   $224.3152   $224.32   $224.30   $224.30  
  Purchase #4 $133.87   4.154%   $139.431   $139.43   $139.45   $139.40  
  Purchase #5 $149.84   6.153%   $159.0597   $159.06   $159.05   $159.10  
  Purchase #6 $170.45   4.261%   $177.7129   $177.71   $177.70   $177.70  
  Purchase #7 $15.87   11.362%   $17.6731   $17.67   $17.65   $17.70  
  7 purchase totals = $846.54       $908.0395   $908.03   $908.00   $908.10