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 $41.96   11.854%   $46.9339   $46.93   $46.95   $46.90  
  Purchase #2 $124.42   9.223%   $135.8953   $135.90   $135.90   $135.90  
  Purchase #3 $154.68   4.753%   $162.0319   $162.03   $162.05   $162.00  
  Purchase #4 $46.76   11.325%   $52.0556   $52.06   $52.05   $52.10  
  Purchase #5 $56.94   3.516%   $58.942   $58.94   $58.95   $58.90  
  Purchase #6 $233.82   3.536%   $242.0879   $242.09   $242.10   $242.10  
  Purchase #7 $173.33   3.279%   $179.0135   $179.01   $179.00   $179.00  
  7 purchase totals = $831.91       $876.9601   $876.96   $877.00   $876.90