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 $52.84   11.323%   $58.8231   $58.82   $58.80   $58.80  
  Purchase #2 $222.57   9.710%   $244.1815   $244.18   $244.20   $244.20  
  Purchase #3 $144.59   5.158%   $152.048   $152.05   $152.05   $152.00  
  Purchase #4 $168.44   5.247%   $177.278   $177.28   $177.30   $177.30  
  Purchase #5 $248.65   7.309%   $266.8238   $266.82   $266.80   $266.80  
  Purchase #6 $196.44   11.351%   $218.7379   $218.74   $218.75   $218.70  
  Purchase #7 $37.58   11.866%   $42.0392   $42.04   $42.05   $42.00  
  7 purchase totals = $1,071.11       $1,159.9315   $1,159.93   $1,159.95   $1,159.80