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 $124.88   7.111%   $133.7602   $133.76   $133.75   $133.80  
  Purchase #2 $187.34   4.452%   $195.6804   $195.68   $195.70   $195.70  
  Purchase #3 $75.54   8.844%   $82.2208   $82.22   $82.20   $82.20  
  Purchase #4 $158.80   7.755%   $171.1149   $171.11   $171.10   $171.10  
  Purchase #5 $246.37   8.277%   $266.762   $266.76   $266.75   $266.80  
  Purchase #6 $209.69   3.790%   $217.6373   $217.64   $217.65   $217.60  
  Purchase #7 $81.58   10.103%   $89.822   $89.82   $89.80   $89.80  
  7 purchase totals = $1,084.20       $1,156.9976   $1,156.99   $1,156.95   $1,157.00