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 $156.53   3.728%   $162.3654   $162.37   $162.35   $162.40  
  Purchase #2 $236.59   13.227%   $267.8838   $267.88   $267.90   $267.90  
  Purchase #3 $24.70   6.443%   $26.2914   $26.29   $26.30   $26.30  
  Purchase #4 $110.65   8.818%   $120.4071   $120.41   $120.40   $120.40  
  Purchase #5 $60.37   6.714%   $64.4232   $64.42   $64.40   $64.40  
  Purchase #6 $221.94   12.104%   $248.8036   $248.80   $248.80   $248.80  
  Purchase #7 $163.42   3.378%   $168.9403   $168.94   $168.95   $168.90  
  7 purchase totals = $974.20       $1,059.1148   $1,059.11   $1,059.10   $1,059.10