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 $38.77   11.708%   $43.3092   $43.31   $43.30   $43.30  
  Purchase #2 $183.65   9.767%   $201.5871   $201.59   $201.60   $201.60  
  Purchase #3 $54.66   6.435%   $58.1774   $58.18   $58.20   $58.20  
  Purchase #4 $168.42   10.290%   $185.7504   $185.75   $185.75   $185.80  
  Purchase #5 $41.31   6.484%   $43.9885   $43.99   $44.00   $44.00  
  Purchase #6 $225.68   8.275%   $244.355   $244.36   $244.35   $244.40  
  Purchase #7 $85.51   5.474%   $90.1908   $90.19   $90.20   $90.20  
  7 purchase totals = $798.00       $867.3584   $867.37   $867.40   $867.50