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 $207.38   13.569%   $235.5194   $235.52   $235.50   $235.50  
  Purchase #2 $97.92   5.854%   $103.6522   $103.65   $103.65   $103.70  
  Purchase #3 $53.79   11.418%   $59.9317   $59.93   $59.95   $59.90  
  Purchase #4 $119.65   5.420%   $126.135   $126.14   $126.15   $126.10  
  Purchase #5 $166.87   3.417%   $172.5719   $172.57   $172.55   $172.60  
  Purchase #6 $59.50   6.649%   $63.4562   $63.46   $63.45   $63.50  
  Purchase #7 $215.65   12.126%   $241.7997   $241.80   $241.80   $241.80  
  7 purchase totals = $920.76       $1,003.0661   $1,003.07   $1,003.05   $1,003.10