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 $76.55   12.703%   $86.2741   $86.27   $86.25   $86.30  
  Purchase #2 $124.81   3.202%   $128.8064   $128.81   $128.80   $128.80  
  Purchase #3 $224.70   9.839%   $246.8082   $246.81   $246.80   $246.80  
  Purchase #4 $64.44   13.402%   $73.0762   $73.08   $73.10   $73.10  
  Purchase #5 $233.99   12.111%   $262.3285   $262.33   $262.35   $262.30  
  Purchase #6 $72.98   10.814%   $80.8721   $80.87   $80.85   $80.90  
  Purchase #7 $161.58   12.596%   $181.9326   $181.93   $181.95   $181.90  
  7 purchase totals = $959.05       $1,060.0981   $1,060.10   $1,060.10   $1,060.10