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 $90.92   10.250%   $100.2393   $100.24   $100.25   $100.20  
  Purchase #2 $177.75   6.775%   $189.7926   $189.79   $189.80   $189.80  
  Purchase #3 $101.29   8.398%   $109.7963   $109.80   $109.80   $109.80  
  Purchase #4 $159.34   12.795%   $179.7276   $179.73   $179.75   $179.70  
  Purchase #5 $21.30   6.868%   $22.7629   $22.76   $22.75   $22.80  
  Purchase #6 $225.36   4.687%   $235.9226   $235.92   $235.90   $235.90  
  Purchase #7 $43.59   3.799%   $45.246   $45.25   $45.25   $45.20  
  7 purchase totals = $819.55       $883.4873   $883.49   $883.50   $883.40