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 $138.58   10.599%   $153.2681   $153.27   $153.25   $153.30  
  Purchase #2 $59.67   13.428%   $67.6825   $67.68   $67.70   $67.70  
  Purchase #3 $208.53   5.737%   $220.4934   $220.49   $220.50   $220.50  
  Purchase #4 $248.77   4.817%   $260.7533   $260.75   $260.75   $260.80  
  Purchase #5 $26.64   10.130%   $29.3386   $29.34   $29.35   $29.30  
  Purchase #6 $149.94   9.453%   $164.1138   $164.11   $164.10   $164.10  
  Purchase #7 $244.84   9.363%   $267.7644   $267.76   $267.75   $267.80  
  7 purchase totals = $1,076.97       $1,163.4141   $1,163.40   $1,163.40   $1,163.50