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 $206.82   7.122%   $221.5497   $221.55   $221.55   $221.50  
  Purchase #2 $242.68   6.166%   $257.6436   $257.64   $257.65   $257.60  
  Purchase #3 $31.71   7.628%   $34.1288   $34.13   $34.15   $34.10  
  Purchase #4 $153.93   8.347%   $166.7785   $166.78   $166.80   $166.80  
  Purchase #5 $129.92   5.804%   $137.4606   $137.46   $137.45   $137.50  
  Purchase #6 $181.50   11.579%   $202.5159   $202.52   $202.50   $202.50  
  Purchase #7 $75.39   8.656%   $81.9158   $81.92   $81.90   $81.90  
  7 purchase totals = $1,021.95       $1,101.9929   $1,102.00   $1,102.00   $1,101.90