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 $143.57   6.766%   $153.2839   $153.28   $153.30   $153.30  
  Purchase #2 $219.39   6.509%   $233.6701   $233.67   $233.65   $233.70  
  Purchase #3 $200.37   7.188%   $214.7726   $214.77   $214.75   $214.80  
  Purchase #4 $63.56   4.672%   $66.5295   $66.53   $66.55   $66.50  
  Purchase #5 $187.85   5.653%   $198.4692   $198.47   $198.45   $198.50  
  Purchase #6 $24.87   7.428%   $26.7173   $26.72   $26.70   $26.70  
  Purchase #7 $211.48   13.512%   $240.0552   $240.06   $240.05   $240.10  
  7 purchase totals = $1,051.09       $1,133.4978   $1,133.50   $1,133.45   $1,133.60