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 $191.82   9.343%   $209.7417   $209.74   $209.75   $209.70  
  Purchase #2 $55.98   10.197%   $61.6883   $61.69   $61.70   $61.70  
  Purchase #3 $78.27   3.753%   $81.2075   $81.21   $81.20   $81.20  
  Purchase #4 $6.68   10.747%   $7.3979   $7.40   $7.40   $7.40  
  Purchase #5 $34.80   11.388%   $38.763   $38.76   $38.75   $38.80  
  Purchase #6 $218.73   7.852%   $235.9047   $235.90   $235.90   $235.90  
  Purchase #7 $177.40   7.290%   $190.3325   $190.33   $190.35   $190.30  
  7 purchase totals = $763.68       $825.0356   $825.03   $825.05   $825.00