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 $92.34   6.678%   $98.5065   $98.51   $98.50   $98.50  
  Purchase #2 $127.50   3.791%   $132.3335   $132.33   $132.35   $132.30  
  Purchase #3 $151.40   13.643%   $172.0555   $172.06   $172.05   $172.10  
  Purchase #4 $89.63   5.308%   $94.3876   $94.39   $94.40   $94.40  
  Purchase #5 $114.51   7.251%   $122.8131   $122.81   $122.80   $122.80  
  Purchase #6 $237.78   12.187%   $266.7582   $266.76   $266.75   $266.80  
  Purchase #7 $166.65   9.160%   $181.9151   $181.92   $181.90   $181.90  
  7 purchase totals = $979.81       $1,068.7695   $1,068.78   $1,068.75   $1,068.80