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 $151.75   12.837%   $171.2301   $171.23   $171.25   $171.20  
  Purchase #2 $25.83   4.354%   $26.9546   $26.95   $26.95   $27.00  
  Purchase #3 $103.64   6.623%   $110.5041   $110.50   $110.50   $110.50  
  Purchase #4 $168.76   11.814%   $188.6973   $188.70   $188.70   $188.70  
  Purchase #5 $225.92   9.403%   $247.1633   $247.16   $247.15   $247.20  
  Purchase #6 $156.50   12.607%   $176.23   $176.23   $176.25   $176.20  
  Purchase #7 $94.55   7.742%   $101.8701   $101.87   $101.85   $101.90  
  7 purchase totals = $926.95       $1,022.6495   $1,022.64   $1,022.65   $1,022.70