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 $98.65   8.813%   $107.344   $107.34   $107.35   $107.30  
  Purchase #2 $165.47   6.770%   $176.6723   $176.67   $176.65   $176.70  
  Purchase #3 $82.82   12.841%   $93.4549   $93.45   $93.45   $93.50  
  Purchase #4 $195.65   12.801%   $220.6952   $220.70   $220.70   $220.70  
  Purchase #5 $131.45   10.210%   $144.871   $144.87   $144.85   $144.90  
  Purchase #6 $166.95   13.762%   $189.9257   $189.93   $189.95   $189.90  
  Purchase #7 $86.99   7.401%   $93.4281   $93.43   $93.45   $93.40  
  7 purchase totals = $927.98       $1,026.3912   $1,026.39   $1,026.40   $1,026.40