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 $188.56   9.151%   $205.8151   $205.82   $205.80   $205.80  
  Purchase #2 $61.60   4.242%   $64.2131   $64.21   $64.20   $64.20  
  Purchase #3 $227.89   9.240%   $248.947   $248.95   $248.95   $248.90  
  Purchase #4 $244.69   9.207%   $267.2186   $267.22   $267.20   $267.20  
  Purchase #5 $36.35   11.158%   $40.4059   $40.41   $40.40   $40.40  
  Purchase #6 $85.83   9.599%   $94.0688   $94.07   $94.05   $94.10  
  Purchase #7 $23.60   3.379%   $24.3974   $24.40   $24.40   $24.40  
  7 purchase totals = $868.52       $945.0659   $945.08   $945.00   $945.00