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 $88.48   8.647%   $96.1309   $96.13   $96.15   $96.10  
  Purchase #2 $168.79   5.834%   $178.6372   $178.64   $178.65   $178.60  
  Purchase #3 $156.85   3.138%   $161.772   $161.77   $161.75   $161.80  
  Purchase #4 $206.56   6.286%   $219.5444   $219.54   $219.55   $219.50  
  Purchase #5 $119.95   10.632%   $132.7031   $132.70   $132.70   $132.70  
  Purchase #6 $244.48   4.866%   $256.3764   $256.38   $256.40   $256.40  
  Purchase #7 $172.65   11.474%   $192.4599   $192.46   $192.45   $192.50  
  7 purchase totals = $1,157.76       $1,237.6239   $1,237.62   $1,237.65   $1,237.60