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 $40.61   6.347%   $43.1875   $43.19   $43.20   $43.20  
  Purchase #2 $173.93   7.377%   $186.7608   $186.76   $186.75   $186.80  
  Purchase #3 $185.39   11.281%   $206.3038   $206.30   $206.30   $206.30  
  Purchase #4 $155.90   12.378%   $175.1973   $175.20   $175.20   $175.20  
  Purchase #5 $27.84   12.591%   $31.3453   $31.35   $31.35   $31.30  
  Purchase #6 $110.79   4.446%   $115.7157   $115.72   $115.70   $115.70  
  Purchase #7 $202.99   12.312%   $227.9821   $227.98   $228.00   $228.00  
  7 purchase totals = $897.45       $986.4925   $986.50   $986.50   $986.50