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 $58.26   8.527%   $63.2278   $63.23   $63.25   $63.20  
  Purchase #2 $40.68   10.418%   $44.918   $44.92   $44.90   $44.90  
  Purchase #3 $150.90   7.121%   $161.6456   $161.65   $161.65   $161.60  
  Purchase #4 $164.45   10.409%   $181.5676   $181.57   $181.55   $181.60  
  Purchase #5 $194.30   6.382%   $206.7002   $206.70   $206.70   $206.70  
  Purchase #6 $123.38   5.803%   $130.5397   $130.54   $130.55   $130.50  
  Purchase #7 $249.73   7.417%   $268.2525   $268.25   $268.25   $268.30  
  7 purchase totals = $981.70       $1,056.8514   $1,056.86   $1,056.85   $1,056.80