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 $185.92   13.612%   $211.2274   $211.23   $211.25   $211.20  
  Purchase #2 $244.56   8.477%   $265.2914   $265.29   $265.30   $265.30  
  Purchase #3 $176.45   11.817%   $197.3011   $197.30   $197.30   $197.30  
  Purchase #4 $89.34   9.690%   $97.997   $98.00   $98.00   $98.00  
  Purchase #5 $45.27   7.114%   $48.4905   $48.49   $48.50   $48.50  
  Purchase #6 $98.68   10.352%   $108.8954   $108.90   $108.90   $108.90  
  Purchase #7 $106.32   12.601%   $119.7174   $119.72   $119.70   $119.70  
  7 purchase totals = $946.54       $1,048.9202   $1,048.93   $1,048.95   $1,048.90