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 $188.77   8.191%   $204.2322   $204.23   $204.25   $204.20  
  Purchase #2 $87.54   8.114%   $94.643   $94.64   $94.65   $94.60  
  Purchase #3 $155.27   6.626%   $165.5582   $165.56   $165.55   $165.60  
  Purchase #4 $159.60   10.573%   $176.4745   $176.47   $176.45   $176.50  
  Purchase #5 $181.38   13.798%   $206.4068   $206.41   $206.40   $206.40  
  Purchase #6 $27.33   11.866%   $30.573   $30.57   $30.55   $30.60  
  Purchase #7 $165.44   10.505%   $182.8195   $182.82   $182.80   $182.80  
  7 purchase totals = $965.33       $1,060.7072   $1,060.70   $1,060.65   $1,060.70