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 $47.35   7.168%   $50.744   $50.74   $50.75   $50.70  
  Purchase #2 $192.27   10.610%   $212.6698   $212.67   $212.65   $212.70  
  Purchase #3 $177.34   9.189%   $193.6358   $193.64   $193.65   $193.60  
  Purchase #4 $224.85   8.123%   $243.1146   $243.11   $243.10   $243.10  
  Purchase #5 $54.82   10.291%   $60.4615   $60.46   $60.45   $60.50  
  Purchase #6 $147.61   7.781%   $159.0955   $159.10   $159.10   $159.10  
  Purchase #7 $115.38   6.595%   $122.9893   $122.99   $123.00   $123.00  
  7 purchase totals = $959.62       $1,042.7105   $1,042.71   $1,042.70   $1,042.70