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 $93.65   10.278%   $103.2753   $103.28   $103.30   $103.30  
  Purchase #2 $233.44   12.355%   $262.2815   $262.28   $262.30   $262.30  
  Purchase #3 $53.45   7.172%   $57.2834   $57.28   $57.30   $57.30  
  Purchase #4 $130.34   6.143%   $138.3468   $138.35   $138.35   $138.30  
  Purchase #5 $33.58   9.195%   $36.6677   $36.67   $36.65   $36.70  
  Purchase #6 $228.60   10.153%   $251.8098   $251.81   $251.80   $251.80  
  Purchase #7 $245.97   10.435%   $271.637   $271.64   $271.65   $271.60  
  7 purchase totals = $1,019.03       $1,121.3015   $1,121.31   $1,121.35   $1,121.30